Cell Signalling and Receptor Mechanisms · USMLE Step 1

Why can a very low concentration of a signaling ligand elicit a large cellular response?

  1. Because the ligand binds permanently and irreversibly to its receptors
  2. Because each individual receptor binds many ligand molecules at once
  3. Because transduction amplifies signal via second messengers and kinase cascades
  4. Because the ligands enter the nucleus to directly switch on many genes
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Correct answer: Because transduction amplifies signal via second messengers and kinase cascades

Signal amplification allows even a few ligand-receptor interactions to generate many second messengers or activate multiple downstream enzymes, leading to large cellular responses.

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